In processes of a variety of industries where surfactants, water-soluble high-molecular compounds, or the like are handled, such as, for example, the fiber industry, dyeing industry, paper and pulp industry, synthetic resin industry, and dye industry, various anti-foaming agents have been used in order to prevent various troubles caused by foaming.
Conventionally used anti-foaming agents, for example, include mineral oils, fats and oils, fatty acids, fatty acid esters, alcohols, silicones, poly(alkylene glycol)s, and mixtures thereof in arbitrary proportions.
These anti-foaming agents can exhibit their anti-foaming effect by being incorporated beforehand into substances that will cause foaming or by being directly added to liquids that are foaming. On the other hand, however, there have been not a few cases where the addition of anti-foaming agents itself causes a problem.
For example, because the known anti-foaming agents generally are insoluble or only slightly soluble in water, use of these may cause the following troubles. That is, in the case where products to which anti-foaming agents have been added are mixed with water to dissolve the products, the anti-foaming agents separate out and float on or in the resulting solutions or the solutions become cloudy due to emulsification. Further, in the field of coatings, adhesives, or the like, pinholes are formed and repelling occurs in coating or adhesive films or the like, and this may impair the adhesion of the films.
Anti-foaming agents of the silicone type, fatty acid ester type, and similar types undergo hydrolysis or other reactions in aqueous solutions with the lapse of time and are thus denatured, so that they not only lose their anti-foaming effect, but form scums and precipitates to cause fouling of the facilities and products.
Although poly(alkylene glycol)-type anti-foaming agents are relatively less apt to cause the above-described troubles, the anti-foaming effect of this type of anti-foaming agents is insufficient in itself.
For the purpose of overcoming these problems, several anti-foaming agents have been developed hitherto.
In JP-A-59-132908 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-60-137405, for example, there are descriptions to the effect that polyoxyalkylene chain-containing compounds which are produced using monoepoxy compounds such as monoglycidyl ethers, as raw material, and have a terminal .alpha.-alkyl glyceryl ether group are useful as an anti-foaming agent for aqueous solutions containing water-soluble high-molecular compounds. However, since the terminal alkyl groups in these compounds have been directly glyceryl-etherified, there are problems that if the anti-foaming agents are added to aqueous solutions of water-soluble high-molecular compounds or the like in amounts that are necessary for the anti-foaming agents to sufficiently exhibit their anti-foaming effect, the clarity of the aqueous solutions is impaired, and that incorporation of these anti-foaming agents into coating compositions or adhesives may cause repelling or pinholes.
As described above, each of the conventionally known anti-foaming agents has both an advantage and a disadvantage, and there is no anti-foaming agent which is comprehensively satisfactory. Hence, development of an anti-foaming agent free of the above described problems has been desired.
The qualities particularly required of anti-foaming agents for water-soluble high-molecular compounds are to produce an excellent long-lasting anti-foaming effect when added even in a small amount and to uniformly dissolve in aqueous solutions of water-soluble high-molecular compounds so as not to impair the clarity of the solutions.
Any of the conventional anti-foaming agents does not possess both of the above qualities and, hence, development of an excellent anti-foaming agent satisfying all of these requirements has long been a subject for eliminating foaming troubles in various industries where water-soluble high-molecular compounds are handled.